A small article discuss why there are so many (good) Debian-based distributions and why Debian is a strong distribution. They go through Libranet, Xandros, Linspire and mention Ubuntu as well.
Read it at enterpriseworkingplanet:Quote:

If you haven't tried Debian, or tried it and got frustrated, I encourage you to give it another look. In my not-very-humble opinion, it has a number of strengths over RPM-based systems:

* Superior package management and quality control * Runs on more hardware architectures than any other Linux * Translated into more languages than any other Linux * Separates Free and Non-Free packages into separate archives, giving users easy selection control * Largest official package archives (currently over 15,000) * You can upgrade a Debian system continuously and indefinitely, without ever needing to reformat and reinstall